The proposed research involves a 5-year systematic study of ticks on a worldwide basis including morphological, cladistic, molecular and genetic analyses. Ticks transmit more pathogens to humans and their animals than any other arthropods, and systematic studies of these disease transmitters are essential to the understanding of vector/host relationships and vectorial capacity. The basis for these systematic investigations in the U.S. National Tick Collection, the world's largest, its companion library on ticks and tick-borne diseases, and computer access to complete biosystematic data on over 122,000 tick collections from throughout the globe. These systematic resources are unique, allowing this type of research nowhere else. Specific aim one will be the study of the primary vectors of Lyme disease, i.e., the Ixodes (I.) ricinus complex of ticks on a global basis. These 15 known or potential vector species will be studied morphologically, morphometrically, and at the molecular level to investigate relationships among the species. Hybridization of Nearctic and Palearctic species will be conducted in Switzerland and/or Russia. Specific aim two will be preparation of a monograph on all 55 species of larval Ixodidae known from the United States. This monograph will fill a significant void, given the importance of ixodid larvae in pathogen maintenance, especially via transovarial transmission from female ticks. Both line drawings and SEM photomicrographs will be used in conjunction with keys. Complete data on hosts, geographical distribution, and medical and veterinary importance for each species will be presented. Specific aim three will be a monographic revision of the 44 known and approximately 20 undescribed species of the genus Ixodes from in Central and South America. Little information is available on Borrelia and Ehrlichia spp from Central and South America. We intend to check archived Ixodes species from this area using PCR methods.